1. Field of the Invention:
The present invention relates to a fuel injection system for internal combustion engines such as diesel engines, and more particularly to an improvement in a control system for such a fuel injection system.
2. Prior Art:
A fuel injection pump having a variable pre-stroke mechanism is known as disclosed in Japanese Patent Laid-open Publication No. 55-131562. The disclosed pump includes a reciprocably movable plunger driven by an engine embodying the pump, and a control sleeve slidably fitted on the plunger and axially movable for adjusting the pre-stroke of the plunger. In such fuel injection pump, a non-uniform velocity cam is used as a motion transfer mechanism between the engine and the plunger so as to reciprocate the plunger at a non-uniform speed, thereby simultaniously changing the fuel injection timing and the fuel injection rate which is in dependency on the advancing velocity of the plunger. To improve the fuel consumption and to reduce the noise and exhaust gas concentration, usually the fuel injection rate is so regulated as to be larger in the low speed operation of the engine than in the ordinary or higher speed operation of the engine.
However, according to the known fuel injection pump, the pre-stroke adjustment and the fuel injection quantity adjustment are conducted separately without any linkage or interrelation therebetween. Accordingly, it is difficult to achieve an accurate fuel injection quantity control. Stated more specifically, the fuel injection rate is increased as the plunger pre-stroke increases even when the plunger effective stroke is constant. As a result, the injection pressure increases and the actual injection quantity also becomes larger by 10-20 mm.sup.3 /stroke and more than that at the low fuel injection rate. In the known fuel injection system, the correction of the actual injection quantity in view of a change in the fuel injection rate is not considered.